Lab manager unable to appropriately add workspace to self.workspaces

[flemingcaleb]

If LabManager sees a workspace ID that is not in the local cache (self.workspaces) of workspaces it is supposed to reach out to the database and update the local cache. The code to check for this case exists, it just calls "self.add_workspace_id()" which doesn't exist. Need to make modifications so that this case is handled correctly.

Steps to reproduce:
Register new workspace to the app (do not restart InfraBot)
Attempt to use !lab command
"LabManager object has no attribute 'add_workspace_id'" error